Tank mix application of copper hydroxide either with cyproconazole or pyraclostrobin fungicides reduced the control of coffee leaf rust

Abstract

Coffee leaf rust (CLR) is a major disease that occurs in all coffee-growing regions, and chemical control is the most effective strategy to control the disease. Usually, this control is based on the application of contact and/or systemic fungicides to the foliage of the plants, and a very common practice is the use of tank-mix solution of fungicides to reduce the costs of the application. The aim of this study was to evaluate the efficacy of mixtures of systemic fungicides (triazoles and strobilurins) and copper hydroxide on the germination of uredospores of Hemileia vastatrix and on the control of CLR. The results showed that the effectiveness of a fungicide can be affected when used in mixtures with another fungicide, resulting in ineffective disease control. When copper hydroxide was combined with cyproconazole, the inhibition of uredospore germination was lower than when copper hydroxide was used alone. For both fungicides pyraclostrobin and cyproconazole, effectiveness in the control of CLR was reduced with the presence of copper hydroxide in the mixture, and this loss in efficacy may be associated with the occurrence of alkaline hydrolysis of the fungicides when they are mixed with copper hydroxide. The findings of this study demonstrate that tank mix application of copper hydroxide either with cyproconazole or pyraclostrobin fungicides reduces the control of CLR, so this practice should be avoided by growers.